Vibrational Raman and infrared spectroscopy are used to probe the dynamical, conformational and packing properties associated with lipid-lipid and lipid-protein interactions in membrane assemblies. For example, a study of a series of mixed-chain phosphatidylcholine multilamellar dispersions indicate that membrane lipids adopt two types of chain conformations in bilayer systems. In the first class the two monolayers pack independently, as typified by C(18):C(18)PC and C(18):C(16)PC bilayers. In contrast, the hydrocarbon chains of C(18):C(10)PC, C(18):C(12)PC and C(18):C(14)PC dispersions interdigitate and couple the two monolayers across the bilayer center.